Apparatus for the production of phosphoric acid

ABSTRACT

THE APPARATUS COMPRISES A DOUBLE-WALLED COMBUSTION TOWER PROVIDED WITH A COVER AND BOUNDED BY AN INSIDE WALL AND AN OUTSIDE WALL SPACED APART FROM ONE ANOTHER. THE INSIDE WALL HAS A BOTTOM SECTION SHAPED AS AND TERMINATING IN A TRUNCATED CONE AND A COMBUSTION NOZZLE OPENING INTO THE COMBUSTION TOWER IS PASED THROUGH THE COVER. AN ACID COLLECTING TANK IS DISPOSED DOWNSTREAM OF THE COMBUSTION TOWER; AND AN IMMERSION TUBE WHICH IS OPEN AT ITS LOWER END IS ARRANGED SO AS TO OPEN INTO THE TRUNCATED COME SECRION OF THE COMBUSTION TOWER.

May 14, 1974 BERG ErAL 3,810,740

APPARATUS FOR THE PRODUCTION OF PHOSPHORIC ACID Filed Dec. 7, 1971United States Patent US. Cl. 23-277 R 6 Claims ABSTRACT OF THEDISCLOSURE The apparatus comprises a double-walled combustion towerprovided with a cover and bounded by an inside wall and an outside wallspaced apart from one another. The inside wall has a bottom sectionshaped as and terminating in a truncated cone and a combustion nozzleopening into the combustion tower is passed through the cover. An acidcollecting tank is disposed downstream of the combustion tower; and animmersion tube which is open at its lower end is arranged so as to openinto the truncated cone section of the combustion tower.

The present invention relates to an apparatus of acidproof metallicmaterial for the production of phosphoric acid by burning yellowphosphorus.

It has been reported earlier that phosphoric acid can be produced in anapparatus of acid-proof steel which substantially comprises, as acombination of a combustion tower with an acid collector, a cylindricalcontainer closed by means of flanged dished heads, and an off-gas outletthat is disposed laterally with respect thereto. With reference to thisapparatus, it should be noted that the supporting structure, in whichthe container is hooked, has to support not only the containers weightbut also the weight of the phosphoric acid accumulating therein, whichis disadvantageous. Furthermore, the container is subject to thermalexpansion and it is accordingly necessary for the acid outlet projectingoutwardly from the containers bottom portion to be provided withcompensators which, however, are susceptible to disturbances. The stepof cooling the container from the outside by spraying water onto it alsois not fully satisfactory. This in view of the fact that it is customaryfor a phosphorus combustion facility to be erected in the open air. As aresult, the container may often be found to be cooled unilaterally onlyas the film of water sprayed onto it may fail to be effective on theside before the wind. The partial evaporation of cooling water on thecontainers outside wall may effect deposition of boiler scale andhandicap the heat exchange through the wall of the container. Inaddition thereto, vapor damp or cooling water may cause inconvenience tothe neighborhood of the combustion means. Still, further, the off-gasoutlet is disposed laterally with respect to the container and thestream of gas is accordingly caused to travel through the combustion andreaction chambers in a direction inclined with respect thereto. As aresult, the off-gas in the lower section of the reaction chamber issprayed irregularly with recycle acid whereby the absorption of P 0 inthe recycle acid is impaired.

It is an object of the present invention to provide a fully satisfactoryapparatus for the production of phosphoric acid by burning yellowphosphorus, the apparatus being designed so as to permit the structuresupporting the container to be released from the weight of thephosphoric acid accumulating downstream of a combustion tower and topermit the outside wall of the combustion tower to be cooled uniformlyby forcing the cooling 'ice water to flow in a predetermined manner. Toachieve this, the invention provides an apparatus which substantiallycomprises a double-walled combustion tower provided with a cover andbounded by an inside wall and an outside wall spaced apart from oneanother, the said inside wall having a bottom section shaped as andterminating in a truncated cone; a combustion nozzle opening into thecombustion tower through said cover; an acid collecting tank disposeddownstream of the said combustion tower; and an immersion tube open atits lower end and opening into the said truncated cone section of thecombustion tower.

Further preferred embodiments of the apparatus of the present invention,which can be used singly or in combination, provide (a) for the upperend of the combustion tower to be booked in a steel structure supportingit;

(b) for the lower section of the combustion tower to be provided with abevelled off-gas conduit opening deeply into the center portion of thetower and projecting outwardly through, and upwardly with respect to,the towers inside and outside walls;

(c) for the acid collecting tank to be provided with an immersion pumpand conduits connecting the pump to an orthodox annular acid-receivingcup in the head portion of the combustion tower, and connecting it toconventional nozzles disposed in the center portion of the combustiontower;

(d) for the immersion tube to be arranged so as to project freely intothe acid collecting tank;

(e) for screw threads to be welded onto the inside wall of thecombustion tower so as to uniformly distribute cooling water in, andfill with cooling water, the space left between the combustion towersinside and outside walls;

(f) for the outside wall to be welded with merely its lower end to thecombustion towers inside wall;

(g) for the outside wall to be comprised of a plurality of,

preferably two, cylindrical jacket sections;

(h) for the jacket sections to be welded with merely their lower ends tothe combustion towers inside wall;

(i) for the off-gas conduit projecting into the center portion of thecombustion tower to be cut off so as to be bevelled downwardly.

By the separate arrangement of the phosphorus combustion chamber and theacid collecting tank, the supporting structure merely has to bear thecombustion tower, which is hooked therein, whilst the acid collectingtank with the phosphoric acid contained therein rests on the floor.Reliable functioning of the combustion tower, which is subject toconsiderable variations in length during the operation and standstillperiods, is ensured firstly by the non-rigid connection existing betweenthe combustion tower and acid collecting tank and secondly by the factthat merely the upper end of the tower is secured to the structuresupporting it. In addition to this, the use of compensators in the acidconduit system is rendered unnecessary by positioning the immersionpump, which is used to circulate the acid, on the acid collecting tank.

To avoid partial evaporation of cooling water and the consequentialdeposition of boiler scale on the walls of the combustion tower, it isnecessary for the space left between the towers inside and outside wallsto be continually and completely filled with water. Screw threads mayadvantageously be placed between, and welded to the towers inside andoutside walls, to ensure the uniform supply of all tower sections withfresh cooling water.

The load exerted against the towers inside wall by the outside pressurewhich results from the static height of the cooling water column can bekept low by subdividing the towers outside wall into a plurality of,preferably two, jacket sections. As a result, the inside wall can bemade thinner which means less expensive of structural materials andsimultaneously means improved abstraction of heat from the interior ofthe tower.

While the towers inside and outside walls are subject to inconsistentthermal expansion, the fact remains that this is no problem if merelythe lower ends of the jacket sections forming the outside wall arewelded to the towers inside wall. By means of the bevelled off-gasconduitthis element is disposed in the lower section of the combustiontower, projects deeply into the towers center portion and is cut offdownwardlyit is possible to render the flow of gas in the combustion andreaction chambers more uniform and thereby to also improve the reactionconditions considerably. Still further, the separation of off-gas fromacid droplets is beneficially influenced -'by breaking turbulence whichis produced upon the introduction of the gas stream into the off-gasconduit and which causes the direction of flow of the gas stream to besharply deflected.

The present invention will now be described with reference to theaccompanying drawing showing a diagrammatic and exemplary form ofapparatus.

As can be seen from the drawing, a combustion tower 2 is hooked in asteel structure supporting it. The combustion tower 2 is bounded by aninside wall 3 provided with a bottom 4, which has the shape of atruncated cone and terminates in an immersion tube 5 having an openlower end, and by an outside wall comprising two jacket sections 6 and7, respectively. Between jacket section 6 and jacket section 7, theinside wall 3 is provided with passageways 8 receiving nozzles whichopen into the towers interior. In its base portion, the combustion tower2 is provided with an olT-gas conduit 9 which is inclined with respectthereto, projects outwardly through the inside wall 3 and jacket section7 and opens deeply into the center portion of tower 2, where it is cutoff downwardly. An immersion tube 5 opens freely into an acid collectingtank 10 which has an immersion pump 11 mounted thereon.

The upper end of inside wall 3 terminates in a semicircular roundedoverflow edge 12. Disposed around the upper end of inside wall 3 andspaced therefrom is an outer collar 13 the lower end of which is securedby means of a circular ring 14 to the inside wall 3 so as to form anacid cup 20. The upper rim portion of outer collar 13 is fast with aconically shaped tower cover 5 having a passageway 16 centrally placedtherein. Passageway 16 supplies fresh air and receives a phosphorussupply line 17 opening into the tower and having a nozzle 18 secured toits lower end. Cover is water-cooled by means of an annular conduit 19which is disposed thereabove and has apertures in its underside. Thecooling water travels via an orifice plate 21 to collecting groove 22,this latter being connected by means of conduit 23 to the towers coolingsystem. The tower is cooled with water which enters the system throughinlet 24 and is forced to flow helically through screw threads 25 whichare disposed between, and welded to, inside wall 3 and jacket section 6.Jacket section 6 has a widened upper end shaped as an annular cup 26delivering water through socket 27 and a conduit 28 to the towers baseportion. In analogous manner, water is forced to flow in the towers baseportion through screw threads 25 disposed between, and welded to, insidewall 3 and jacket section 7, and delivered to an annular cup 29, fromwhere it is removed through an outlet 30.

The acid-receiving cup and the nozzles opening into the towers interiorthrough passageways 8 are supplied with phosphoric acid circulated bymeans of immersion pump 11 causing the acid to flow through conduits 31,33 and 34, and a heat exchanger 32. Acid cup 20 is coutinually filledwith acid. To ensure this, conduit 34 is provided with a gooseneck 35and a vent pipe 36. To avoid the escape of splashes of acid, vent pipe36 is connected to a conduit 37 terminating in cover 15.

The claims:

1. An apparatus for the production of phosphoric acid by burning yellowphosphorus by means of a combustion nozzle in an acid-proof metalcombustion tower having an acid collecting tank associated therewith,the apparatus comprising a combustion tower having a doublewalled uppersection and middle section bounded by an inside wall and an outsidewall, the walls being spaced apart, and a single-walled lower sectionbounded by the inside wall having a lower portion terminating in atruncated cone which in turn terminates in an immersion tube, theimmersion tube being open at its lower end and projecting freely intothe acid collecting tank bounded by a top wall, being disposed and beingsupported separately from, and downstream of the combustion tower; sealsbetween the immersion tube and the top wall of the acid collecting tank;the combustion tower being hooked near its upper end in a steelsupporting structure to provide a non-rigid connection with the acidcollecting tank to release the steel supporting structure from theWeight of the phosphoric acid in the acid collecting tank; an immersionpump being freely mounted on the acid collecting tank so as to projectthereinto; seals between the immersion pump and the top wall of the acidcollecting tank; the upper section of the combustion tower having anannular acid-receiving cup, nozzles disposed in the middle section ofthe combustion tower, an acid conduit system free from compensatorsconnecting the immersion pump to the annular acid-receiving cup disposedin the upper section of the said combustion tower, and furtherconnecting the said pump to the nozzles disposed in the middle sectionof the combustion tower; and an off-gas conduit inclined with respect tothe combustion tower projecting through the inside wall and the outsidewall of the combustion tower so as to deeply and centrally reachthereinto, the off-gas conduit having an inclined end and bevelleddownwardly.

2. The apparatus as claimed in claim 1, wherein screw threads are weldedto the inside wall of the combustion tower so as to uniformly distributecooling water in, and fill with cooling water, the space left betweenthe combustion towers inside and outside walls.

3. The apparatus as claimed in claim 1, wherein the outside wall iswelded with merely its lower end to the combustion towers inside wall.

4. The apparatus as claimed in claim 1, wherein the outside wall iscomprised of a plurality of cylindrical jacket sections.

5. The apparatus as claimed in claim 4, wherein the outside wall iscomprised of two cylindrical jacket sections.

6. The apparatus as claimed in claim 4, wherein the jacket sections arewelded with merely their lower ends to the combustion towers insidewall.

References Cited UNITED STATES PATENTS 3,526,482 9/1970 Beltz ct a1.23--283 3,064,408 11/1962 Erga et a1. 26l-115 X 2,708,620 5/1955Winnicki 23262 X 858,062 6/1907 Day 23-262 JAMES H. TAYMAN, 111.,Primary Examiner U.S. C1. X.R.

